Silica glass is used for a lens, a prism, and a photomask in a projection aligner (a lithography apparatus) for manufacturing large-scale integration (LSI), a display TFT substrate, a lamp tube, a window material, a reflector, a semiconductor industrial cleaning container, a silicon semiconductor melt container, and others. However, as a raw material of the silica glass, a compound such as expensive silicon tetrachloride must be used, and a silica glass melting temperature or processing temperature is as considerably high as approximately 2000° C., energy consumption is hence high, and a cost rises. Therefore, a silica glass manufacturing method using a relatively inexpensive powder raw material has been conventionally considered.
For example, Patent Literature 1 discloses a method for hydrolyzing silicon alkoxide to provide silica sol, gelling the silica sol to provide wet gel, drying this gel to provide dry gel, and finally performing high-temperature sintering to obtain a transparent silica glass body (a sol-gel method). Furthermore, Patent Literature 2 discloses a method for obtaining transparent silica glass from a silica sol mixed solution made of tetramethoxysilane or tetraethoxysilane and a silica sol solution containing silica fine particles by the sol-gel method. Moreover, Patent Literature 3 discloses that, in a method for manufacturing transparent silica glass by using silicon alkoxide and silica glass fine particles as main raw materials, a heating treatment at a temperature of 200° C. to less than 130° C. is carried out in an oxygen gas containing atmosphere, a heating treatment for raising the temperature to 1700° C. or more is performed in a hydrogen gas containing atmosphere, and a reduced-pressure atmosphere heating treatment is effected between the two heating treatments. However, these conventional sol-gel methods have a problem in a dimensional accuracy of fabricated silica glass at an early stage or heat resisting properties during subsequent use at a high temperature, and their costs are not very low.
Additionally, Patent Literature 4 discloses a method for obtaining a silica containing complex by mixing at least two types of silica glass particles having different characteristics, e.g., a silica glass fine powder and silica glass particles to provide a water containing suspension, then performing compression molding, and effecting sintering at a high temperature (a slip-cast method). Further, Patent Literature 5 discloses a method for fabricating an opaque silica glass composite based on fabrication of a liquid mixture (slurry) containing silica glass particles having a size of 100 μm or less and silica glass granules having a size of 100 μm or more, injection into a molding die, subsequent drying, and sintering. However, according to these conventional slip-cast methods, a compact greatly contracts during a drying process or a sintering process, and a silica glass compact having a high dimensional accuracy and a large thickness cannot be created.
Even now, as a method for manufacturing a silica crucible for LSI single crystal silicon manufacture, such manufacturing methods as described in Patent Literatures 6 and Patent Literature 7 are used. Each of these methods is a method for putting a quartz powder or a synthetic cristobalite powder subjected to an ultra-high purity treatment into a rotating mold, performing molding, then pushing electrodes from above, applying electric power to the electrodes to cause arc discharge, and increasing an atmospheric temperature to a melting temperature zone (which is assumed to be approximately 1800 to 2100° C.) of the quartz powder, thereby melting and sintering the quartz raw material powder.
However, these manufacturing methods have a problem of high costs since the quartz raw material powder having super-high purity is used. Further, when the manufactured silica crucible is used, there occurs such a problem in manufacturing cost and silicon crystal quality that the molten silicon reacts with the silica crucible to produce SiO gas, and this gas is taken into silicon crystal as gaseous bubbles. Moreover, there also arises a problem in heat deformation properties of the silica crucible that a sidewall of the crucible is softened and deformed at the time of pulling the single-crystal silicon.
Additionally, Patent Literature 8 discloses a silica crucible having a three-layer configuration including an outer layer made of natural quartz glass, an intermediate layer made of synthetic quartz glass having high aluminum concentration, and an inner layer made of a high-purity synthetic quartz glass based on an arc discharge melting method of silica powder raw materials (an atmosphere at the time of melting is assumed to be air). Further, an impurity movement preventing effect using the intermediate layer is disclosed. However, in the three-layer configuration based on such a configuration, not only costs are high, but also a problem of gaseous bubbles in manufactured silicon crystal has not been solved.
Furthermore, Patent Literature 9 discloses technology that reduces gaseous bubbles in a molten quartz crucible wall by performing pressure reduction and suction from the periphery of a molding die at the time of arc discharge melting of a silica powder raw material compact. However, a dissolved gas in a silica crucible wall cannot be completely removed by just performing pressure reduction and suction of air that is present in a temporary compact of the silica powder. Moreover, when a silica crucible is used, there occurs a problem that molten silicon reacts with the silica crucible to produce SiO gas and this gas is taken into silicon crystal as gaseous bubbles.
Additionally, Patent Literature 10 discloses a quartz glass crucible that can avoid cavity defects that are produced when bubbles of SiO gas are taken into silicon single crystal. As its means, irregularities provided by forming many scratches on at least part of inner surfaces of a straight body portion and a curved portion of the crucible at a depth of 50 μm to 450 μm. However, when the surfaces having such irregularities are provided, degasification of the generated SiO gas to the outside of the silica container is insufficient, and it is difficult to sufficiently reduce voids or non-pierced small-diameter holes (pinholes) in a silicon wafer producing by slicing and polishing this silicon single crystal.